1. Field of the Invention
The present general inventive concept relates to an image forming apparatus and a control method thereof, and, more particularly, to an image forming apparatus and a control method thereof, in which the color balance of a scanned image is corrected through an offset correction for an image signal output from an image sensor module, to achieve an enhancement in image quality.
2. Description of the Related Art
An image forming apparatus is well known for scanning an image of a document, creating image data, and rendering the image data into a visual image on paper. Various image forming apparatuses having various functions are known. Examples of such image forming apparatuses include a printer, a scanning unit, a facsimile machine, a copy machine and a complex machine having the functions of the above-mentioned appliances.
A general image forming apparatus, for example, a scanning unit, includes a stage glass, on which a document is laid, and a scanning head to read an image of the document while reciprocating beneath the stage glass. The scanning head includes a light source module to scan light to the document, and an image sensor to detect light reflected from the document and to convert the detected light to an image signal. The image sensor may be implemented through a charge coupled device (CCD) or a constant image sensor (CIS).
In the general image forming apparatus, the image signal generated from the image sensor may be distorted due to a deviation in the amount of light generated from the light source module or a non-uniformity of the light amount. Such a phenomenon is called “shading.” Due to such a shading phenomenon, an image signal having a shape different from the image of the document may be generated. Therefore, it is necessary to correct the shading phenomenon incurred in the image signal. In a typical shading correction method, a white reference sheet provided at one side of a flat bed is scanned prior to the scanning of a document, to obtain reference shading data. An image signal, which is obtained in accordance with the scanning of the document, is then compared with the reference shading data, to determine black or white pixels. Based on the determined black or white pixels, shading correction is executed.
Meanwhile, the signal output from the image sensor, which has the form of an analog signal, has an offset value due to the physical characteristics of the circuit of the image sensor. In particular, when the image sensor includes R, G, and B channels, signals output from the R, G, B channels have offset values having different levels as they pass through independent circuits, respectively. For this reason, black reference shading data for one channel is different from those for other channels. As a result, the signals output from respective channels exhibit an amplified level difference as they are processed through an image pre-processing procedure. Consequently, the scanned image exhibits color shift.